Heat pump heating system

ABSTRACT

A heat pump heating system ( 1 A) includes: a refrigerant circuit ( 3 ) including a compressor ( 21 ), a radiator ( 22 ), and an expansion member ( 25 A), and an evaporator ( 26 ); a circulation path ( 5 ) for circulating a liquid through the radiator ( 22 ) to produce a heated liquid; and a heater ( 4 ) for dissipating heat of the heated liquid. The refrigerant circuit ( 3 ) is provided with an internal heat exchanger ( 23 A) for transferring heat from a high pressure refrigerant that has released heat in the radiator ( 22 ) to a low pressure refrigerant. The liquid flowing through the circulation path ( 5 ) is cooled in a liquid cooling heat exchanger ( 24 ) by means of the high pressure refrigerant flowing out of the internal heat exchanger ( 23 A), before the liquid flows into the radiator ( 22 ).

TECHNICAL FIELD

The present invention relates to a heat pump heating system forperforming heating through the use of a heated liquid produced by a heatpump (refrigeration cycle apparatus).

BACKGROUND ART

Conventionally, there has been known a heat pump heating system forproducing hot water by a heat pump and performing heating through theuse of this hot water. For example, Patent Literature 1 discloses a heatpump heating system 100 as shown in FIG. 10. This heat pump heatingsystem 100 includes a heat pump 200 having a refrigerant circuit 10 forcirculating a refrigerant and a circulation path 16 for circulatingwater.

The refrigerant circuit 10 includes a compressor 11, a radiator 12, anexpansion valve 13, and an evaporator 14, which are connected in thisorder by pipes. The circulation path 16 has a hot water storage tank 15.Water is taken out of the hot water storage tank 15 and fed to theradiator 12, where hot water is produced. This hot water is stored inthe hot water storage tank 15. The hot water stored in the hot waterstorage tank 15 is fed to, for example, a heater 17 disposed in a room,releases heat there, and then is returned to the hot water storage tank15.

Recently, there have been proposals to provide an internal heatexchanger in a heat pump. For example, Patent Literature 2 discloses, asa heat pump for hot water supply, a heat pump 201 including an internalheat exchanger 18 as shown in FIG. 11. The internal heat exchanger 18 isdesigned to exchange heat between a high pressure refrigerant flowingout of a radiator 12 and a low pressure refrigerant flowing out of anevaporator 14. With this structure, the temperature of the low pressurerefrigerant drawn into a compressor 11 increases, which produces highertemperature hot water.

Furthermore, Patent Literature 3 discloses a heat pump 202 as shown inFIG. 12A. This heat pump 202 is provided with a first radiator 12A and asecond radiator 12B as radiators for allowing a refrigerant to releaseheat. A high pressure refrigerant that has released heat in the firstradiator 12A releases heat in the internal heat exchanger 18, and thenis introduced into the second radiator 12B and further releases heatthere. On the other hand, water flowing through a flow path 19 is heatedin the second radiator 12B and then further heated in the first radiator12A, as shown in FIG. 12B.

CITATION LIST Patent Literature

Patent Literature 1 JP 2008-039306 A

Patent Literature 2 JP 2006-300487 A

Patent Literature 3 JP 2002-162123 A

SUMMARY OF INVENTION Technical Problem

In the heat pump heating system 100 shown in FIG. 10, for example,during a long heating operation, in some cases, the temperature of waterdoes not decrease so much in the heater 17 and medium temperature water(for example, at about 40° C. to 60° C.) is supplied to the radiator 12of the heat pump 200. When such medium temperature water is supplied tothe radiator 12, however, the heat exchange efficiency of the radiator12 decreases, resulting in a decrease in the COP (Coefficient ofPerformance) of the heat pump 200. This problem also occurs when theheat pump 201 shown in FIG. 11 or the heat pump 202 shown in FIG. 12A isused as a heat pump for the heat pump heating system 100 shown in FIG.10.

The present invention has been made in view of the above problem, and itis an object of the present invention to improve the COP of a heat pumpin a heat pump heating system even if a medium temperature liquid is fedto the heat pump.

Solution to Problem

In order to solve the above problem, the present invention provides aheat pump heating system including: a refrigerant circuit including acompressor for changing a low pressure refrigerant to a high pressurerefrigerant, a radiator for allowing the high pressure refrigerant torelease heat, an expansion member for changing the high pressurerefrigerant to the low pressure refrigerant, and an evaporator forallowing the low pressure refrigerant to absorb heat; a circulation pathfor circulating a liquid through the radiator to produce a heatedliquid; a heater for dissipating heat of the heated liquid; an internalheat exchanger, provided in the refrigerant circuit, for transferringheat from the high pressure refrigerant that has released heat in theradiator to the low pressure refrigerant; and a liquid cooling heatexchanger for cooling the liquid flowing through the circulation path bymeans of the high pressure refrigerant flowing out of the internal heatexchanger, before the liquid flows into the radiator.

Advantageous Effects of Invention

According to the heat pump heating system of the present inventionconfigured as described above, a low temperature liquid can beintroduced into the radiator even if the temperature of the liquid ismedium when it is fed to the heat pump. Therefore, the COP of the heatpump can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic configuration diagram of a heat pump heatingsystem according to a first embodiment of the present invention.

FIG. 2 is a Mollier diagram of a heat pump used in the heat pump heatingsystem shown in FIG. 1.

FIG. 3 is a schematic configuration diagram of a heat pump heatingsystem according to a modification of the first embodiment of thepresent invention.

FIG. 4 is a schematic configuration diagram of a heat pump heatingsystem according to a second embodiment of the present invention.

FIG. 5 is a Mollier diagram of a heat pump used in the heat pump heatingsystem shown in FIG. 4.

FIG. 6 is a schematic configuration diagram of a heat pump heatingsystem according to a third embodiment of the present invention.

FIG. 7 is a schematic configuration diagram of a heat pump heatingsystem according to a fourth embodiment of the present invention.

FIG. 8 is a schematic configuration diagram of a heat pump heatingsystem according to a fifth embodiment of the present invention.

FIG. 9 is a schematic configuration diagram of a heat pump heatingsystem according to a sixth embodiment of the present invention.

FIG. 10 is a schematic configuration diagram of a conventional heat pumpheating system.

FIG. 11 is a schematic configuration diagram of a conventional heatpump.

FIG. 12A is a schematic configuration diagram of another conventionalheat pump, and FIG. 12 B is a graph showing the temperatures of arefrigerant and water passing through first and second radiators in theheat pump shown in FIG. 12A.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

First Embodiment

FIG. 1 shows a heat pump heating system 1A according to the firstembodiment of the present invention. This heat pump heating system 1Aincludes a heat pump 20A having a refrigerant circuit 3 for circulatinga refrigerant, a circulation path 5 for circulating a liquid, and acontroller 6 for controlling the elements totally.

The circulation path 5 is designed to circulate the liquid through aradiator 22 described later to produce a heated liquid. In the presentembodiment, a heater 4 for dissipating the heat of the heated liquid isincorporated in the circulation path 5, so that the liquid is circulatedwithout stopping and the heated liquid thus produced releases heatdirectly in the heater 4. That is, the circulation path 5 also serves asa heating circuit.

In the present embodiment, water is used as the liquid serving as a heatcarrier. The liquid of the present invention is not necessarily limitedto this. Any liquid can be used as long as it can receive heat from therefrigerant circulating through the refrigerant circuit 3 and releaseheat into the atmosphere in the heater 4. As the liquid, for example, anantifreeze mixture of propylene glycol or the like and water can beused. The following description will be made on the assumption that theliquid is water and the heated liquid is hot water.

The refrigerant circuit 3 includes a compressor 21 for changing a lowpressure refrigerant to a high pressure refrigerant, a radiator 22 forallowing the high pressure refrigerant to release heat, an expansionvalve 25A serving as an expansion member for changing the high pressurerefrigerant to the low pressure refrigerant, an evaporator 26 forallowing the low pressure refrigerant to absorb heat, and first tofourth pipes 31 to 34 connecting these devices in this order. In theradiator 22, heat is exchanged between the water passing through theradiator 22 and the refrigerant, and thereby the water is heated. In theevaporator 26, heat is exchanged between the refrigerant and air blownby a fan 26 a, and thereby the refrigerant absorbs heat. In the presentembodiment, the refrigerant circuit 3 is filled with carbon dioxide,which reaches a supercritical state on the high pressure side, as therefrigerant. An internal heat exchanger 23A is provided in therefrigerant circuit 3 so as to bundle the second pipe 32 and the fourthpipe 34. A liquid cooling heat exchanger 24 is provided on thedownstream side of the internal heat exchanger 23A in the second pipe32.

The internal heat exchanger 23A is designed to exchange heat between thehigh pressure refrigerant flowing out of the radiator 22 and the lowpressure refrigerant flowing out of the evaporator 26 so as to transferheat from the high pressure refrigerant that has released heat in theradiator 22 to the low pressure refrigerant. The liquid cooling heatexchanger 24 is designed to cool the water flowing through thecirculation path 5 by means of the high pressure refrigerant flowing outof the internal heat exchanger 23A, before the water flows into theradiator 22.

The heater 4 is designed to heat, for example, a room by heatdissipation from hot water. As the heater 4, for example, a heatdissipating device to be placed in a room may be used. A hot water panelto be laid on a floor also may be used.

The circulation path 5 includes a supply pipe 51 for introducing thewater from the heater 4 to the liquid cooling heat exchanger 24, anintermediate pipe 52 for introducing the water from the liquid coolingheat exchanger 24 to the radiator 22, and a recovery pipe 53 forintroducing the water in the form of hot water from the radiator 22 tothe heater 4. In the present embodiment, the supply pipe 51 is providedwith a pump 62. The supply pipe 51 is further provided with atemperature sensor 61 for detecting the temperature of the water flowinginto the supply pipe 51 from the heater 4.

The intermediate pipe 52 and the downstream part of the pump 62 in thesupply pipe 51 are connected by a bypass pipe 54. Specifically, thesupply pipe 51 is provided with a three-way valve 63, and the upstreamend of the bypass pipe 54 is joined to this three-way valve 63. Thedownstream end of the bypass pipe 54 is joined to the middle of theintermediate pipe 52.

The three-way valve 63 is designed to switch between a circulation ofthe water not through the bypass pipe 54, that is, a circulation of thewater passing through both of the liquid cooling heat exchanger 24 andthe radiator 22, and a circulation of the water through the bypass pipe54, that is, a circulation of the water passing only through theradiator 22. The three-way valve 63 corresponds to the switching memberof the present invention. It should be noted that the switching memberof the present invention is not necessarily be the three-way valve 63.For example, the switching member may be replaced by an on-off valveprovided in the bypass pipe 54 and an on-off valve provided in thedownstream of the point of the supply pipe 51 to which the bypass pipe54 is joined.

The controller 6 is composed of a microcomputer, a DSP (digital signalprocessor), or the like, and is connected to the above-mentioned heatpump 20A, and the pump 62, the temperature sensor 61, and the three-wayvalve 63.

Next, the control performed by the controller 6 is describedspecifically.

When a user turns on a heating switch (not shown), for example, thecontroller 6 operates the heat pump 20A and rotates the pump 62.Thereby, the water is heated in the radiator 22 to produce hot water,and this hot water is fed to the heater 4 to perform heating.

During this heating operation, the controller 6 uses the temperaturesensor 61 to monitor the temperature of the water flowing into thesupply pipe 51. When the water temperature detected by the temperaturesensor 61 is lower than a predetermined temperature (for example, 20°C.) (hereinafter referred to as a “low temperature condition”), thecontroller 6 controls the three-way valve 63 so that the water iscirculated through the bypass pipe 54. Specifically, the controller 6sets the three-way valve 63 so that the bypass pipe 54 is communicatedwith the upstream part 51 a of the three-way valve 63 in the supply pipe51. As a result, the first route passing only through the radiator 22 isselected.

In the low temperature condition, the refrigerant circulating throughthe refrigerant circuit 3 operates in the following manner. Therefrigerant is compressed by the compressor 21 to a high temperature andhigh pressure state, and then the resulting refrigerant flows into theradiator 22, where it transfers heat to the water flowing through thecirculation path 5. After flowing out of the radiator 22, therefrigerant flows into the internal heat exchanger 23A, where it furthertransfers heat to the refrigerant flowing out of the evaporator 26.After flowing out of the internal heat exchanger 23A, the refrigerantpasses through the liquid cooling heat exchanger 24 while maintainingits state, and is decompressed by the expansion valve 25A to expand to alow temperature and low pressure state. The expanded refrigerant flowsinto the evaporator 26, where it absorbs heat from air. After flowingout of the evaporator 26, the refrigerant flows into the internal heatexchanger 23A, where it further absorbs heat from the refrigerantflowing out of the radiator 22. After flowing out of the internal heatexchanger 23A, the refrigerant is drawn into the compressor 21 again andcompressed there.

On the other hand, the water circulating through the circulation path 5(first route) is heated in the radiator 22, and the resulting hot waterflows into the heater 4 and releases heat to the atmosphere. Afterreleasing heat in the heater 4, the water flows into the radiator 22again and is heated to hot water.

Conversely, when the water temperature detected by the temperaturesensor 61 is equal to or higher than the above predetermined temperature(hereinafter referred to as a “medium temperature condition”), thecontroller 6 controls the three-way valve 63 so that the water iscirculated not through the bypass pipe 54. Specifically, the controller6 sets the three-way valve 63 so that the upstream part 51 a and thedownstream part 51 b of the three-way valve 63 in the supply pipe 51 arecommunicated with each other. As a result, the second route passingthrough both of the liquid cooling heat exchanger 24 and the radiator 22is selected.

In the medium temperature condition, the water flowing into the liquidcooling heat exchanger 24 has a higher temperature than the refrigerantflowing into the liquid cooling heat exchanger 24. The refrigerantcirculating in the refrigerant circuit 3 operates in the followingmanner. The refrigerant is compressed by the compressor 21 to a hightemperature and high pressure state, and then the resulting refrigerantflows into the radiator 22, where it transfers heat to the water flowingthrough the circulation path 5. After flowing out of the radiator 22,the refrigerant flows into the internal heat exchanger 23A, where itfurther transfers heat to the refrigerant flowing out of the evaporator26. After flowing out of the internal heat exchanger 23A, therefrigerant flows into the liquid cooling heat exchanger 24, where itexchanges heat with the water flowing through the circulation path 5. Asa result, the refrigerant is heated almost to the temperature of thewater flowing into the liquid cooling heat exchanger 24. After flowingout of the liquid cooling heat exchanger 24, the refrigerant isdecompressed by the expansion valve 25A to expand to a low temperatureand low pressure state. Then, it flows into the evaporator 26, where itabsorbs heat from air. After flowing out of the evaporator 26, therefrigerant flows into the internal heat exchanger 23A, where it furtherabsorbs heat from the refrigerant flowing out of the radiator 22. Afterflowing out of the internal heat exchanger 23A, the refrigerant is drawninto the compressor 21 again and compressed there.

On the other hand, the water circulating through the circulation path 5(second route) is heated in the radiator 22, and the resulting hot waterflows into the heater 4 and releases heat to the atmosphere and becomesmedium temperature water. After flowing out of the heater 4, the mediumtemperature water flows into the liquid cooling heat exchanger 24, whereit exchanges heat with the refrigerant flowing out of the internal heatexchanger 23A. As a result, the water is cooled to a low temperaturestate. The low temperature water flows into the radiator 22 again, andis heated to hot water.

FIG. 2 shows a Mollier diagram of the heat pump 20A used in the presentembodiment, under the medium temperature condition. In this diagram, abroken line shows a Mollier diagram of the heat pump 201 without theliquid cooling heat exchanger, as shown in FIG. 11. Points A to F inFIG. 2 represent the states at “x” marks A to F in FIG. 1.

In the heat pump 201 without the liquid cooling heat exchanger, shown inFIG. 11, as the refrigerant passes through the radiator, the temperatureof the refrigerant falls from a high temperature Td′ (Point B′)resulting from the compressor to a temperature T_(GC)′ (Point C′) thatis about a temperature Tw1 of the medium temperature water returningfrom the heater. After passing through the radiator, the refrigerantfurther lowers its temperature in the internal heat exchanger and thenis decompressed by the expansion valve. The enthalpy of the decompressedrefrigerant increases from H2′ (Point F′) to H1′ (Point G′) as therefrigerant passes through the evaporator, and further increases as itpasses through the internal heat exchanger.

On the other hand, in the heat pump 20A used in the present embodiment,since the water to flow into the radiator 22 is cooled in the liquidcooling heat exchanger 24, the temperature of the water is Tw2 (<Tw1).Accordingly, the temperature of the refrigerant at the outlet of theradiator 22 is T_(GC) (Point C), which is lower than that in theconventional heat pump 201. After passing through the radiator 22, therefrigerant lowers its temperature to T_(IH) (Point D) in the internalheat exchanger 23A, and then is warmed to T_(EX) (Point E) by the liquidcooling heat exchanger 24. Then, the refrigerant is decompressed by theexpansion valve 3. As shown in this diagram, the enthalpy H2 (Point F)of the decompressed refrigerant is higher than that H2′ in theconventional heat pump 201 (H2>H2′) because the refrigerant isdecompressed after it is heated by the liquid cooling heat exchanger 24.Therefore, the enthalpy increment (ΔH=H1−H2) in the evaporator 4 issmaller than that (ΔH′=H1′−H2′) in the conventional heat pump 201.

As described above, in the heat pump heating system 1A of the presentembodiment, low temperature water can be introduced into the radiator 22even if the temperature of the water is medium when it is fed to theheat pump 20A. Therefore, the COP of the heat pump 20A can be improved.

Furthermore, according to the present embodiment, the temperature of therefrigerant at the outlet of the radiator 22 can be reduced to a lowerlevel than that in the conventional heat pump 201. Therefore, theoptimum high pressure (high pressure at which the COP of the heat pumpis highest) for the temperature of the refrigerant at the outlet of theradiator 22 can be lowered. Accordingly, the differential pressurebetween the high pressure and the low pressure of the refrigerationcycle can be reduced, and thus the differential pressure force appliedto the compression part of the compressor 21 can be lessened. As aresult, the leakage loss of the refrigerant and the friction loss arereduced, and thus the efficiency of the compressor 21 can be improved.In addition, since the high pressure of the refrigeration cycle can belowered, the reliability of the refrigerant circuit 3 also can beimproved. Moreover, the pressure resistance strength required for theconstituent components can be reduced, and therefore the heating systemcan be manufactured at lower cost.

Furthermore, since the discharge pressure of the compressor 21decreases, the temperature of the refrigerant discharged from thecompressor 21 can be lowered. Therefore, the deterioration of thecomponents caused by the discharged high temperature refrigerant can bereduced, and the reliability of the elements can be improved.Particularly in the case where the outside temperature dropssignificantly (to about −5° C. to −15° C.), the problem of an increasein the temperature of the refrigerant discharged from the compressor canbe addressed effectively.

Furthermore, since the enthalpy increment in the evaporator 26 issmaller, the low pressure is higher than that of the conventional heatpump 201. Therefore, the differential pressure between the high pressureand the low pressure of the refrigeration cycle can further be reduced,and thus the differential pressure force applied to the compression partof the compressor 21 can further be lessened. Moreover, since thepressure inside the evaporator 26 increases, the average temperature ofthe evaporator 26 rises. As a result, when frost forms, the load ofdefrosting operation can be reduced, and thus the energy consumed by theheat pump 20A can be reduced and the efficiency of the elements can beimproved.

The heat pump 202 disclosed in Patent Literature 3 and shown in FIG. 12Aapparently seems to have a configuration similar to that of the heatpump 20A of the present embodiment. In the heat pump 202 of PatentLiterature 3, however, the first radiator 12A and the second radiator12B are disposed with the internal heat exchanger 18 being interposedtherebetween, and the temperature of the refrigerant only continues tofall and the temperature of the water only continues to rise, as shownin FIG. 12B, which is distinctly different from the action of the heatpump 20A of the present embodiment. Furthermore, Patent Literature 3 notonly fails to describe the circulation of water but also fails todescribe that the water in the form of medium temperature water isreturned to the heat pump.

In the present embodiment, the bypass pipe 54 and the three-way valve 63serving as a switching member are provided to select the circulation ofthe water through either the first route or the second route. However,these members may be omitted so that the water always passes throughboth of the liquid cooling heat exchanger 24 and the radiator 22.However, it is preferable to provide the bypass pipe 54 and theswitching member in the circulation path 5, as in the presentembodiment, for the following reasons: the water can be prevented frombeing heated in the liquid cooling heat exchanger 24 by passing throughthe second route when the water temperature detected by the temperaturesensor 61 is lower than a predetermined temperature; and the efficiencyof the refrigeration cycle can be kept high by switching the first routeand the second route so that the temperature of the water flowing intothe radiator 22 is lowered as much as possible.

The liquid cooling heat exchanger 24 and the radiator 22 used in thepresent embodiment are both heat exchangers for exchanging heat betweenwater and a refrigerant. Therefore, these devices 24 and 22 can also bemanufactured integrally as a single water-refrigerant heat exchanger. Inthis case, the refrigerant flow path and the water flow path included inthe water-refrigerant heat exchanger each can be divided into two. Withthis structure, a compact heat exchanger can be designed. Therefore, notonly the unit (for example, a heat pump unit) in the heating system canbe downsized but also the manufacturing cost can be reduced.

<Modification>

In the embodiment described above, hot water heated in the refrigerantcircuit 3 releases heat to the atmosphere in the heater 4. The heater 4also may be used as a heating source for hot water supply or snowmelting. Needless to say, the same advantageous effects as above areobtained in these applications.

In the embodiment described above, carbon dioxide is used as therefrigerant. Any refrigerant can be used in the present invention aslong as it has the property of decreasing the optimum high pressure asits temperature at the outlet of the radiator 22 decreases. Furthermore,since the difference between the temperature of the refrigerant at theinlet of the radiator 22 and that at the outlet of the radiator 22increases as the temperature of the refrigerant at the outlet of theradiator 22 decreases, the heat exchange efficiency of the radiator 22is improved, and as a result, the high pressure drops. Therefore,needless to say, the same advantageous effects as above are obtainedeven if the refrigerant, like a fluorocarbon refrigerant, does not reacha supercritical state on the high pressure side during the normaloperation.

Furthermore, in the embodiment described above, the internal heatexchanger 23A is used to exchange heat between the high pressurerefrigerant flowing out of the radiator 22 and the low pressurerefrigerant flowing out of the evaporator 26. Instead, an internal heatexchanger 23B may be used to exchange heat between the high pressurerefrigerant flowing out of the radiator 22 and the low pressurerefrigerant before flowing into the evaporator 26, as shown in FIG. 3.

Alternatively, the compressor 21 may include a main compressor and anauxiliary compressor connected in parallel thereto.

It should be noted that the above modification can also be applied tothe embodiments below.

Second Embodiment

FIG. 4 shows a heat pump heating system 1B according to the secondembodiment of the present invention. As shown in FIG. 4, the heat pumpheating system 1B of the second embodiment has the almost sameconfiguration as the heat pump heating system 1A of the firstembodiment. Therefore, the same reference numerals are assigned to thecomponents having the same functions, and no further description of thesame configuration and operation is given. The same description is notrepeated also in the third to fifth embodiments described below.

The only difference between the heat pump heating system 1B of thepresent embodiment and the heat pump heating system 1A of the firstembodiment is that in the former system 1B, an expander 25B forrecovering power from an expanding refrigerant is used as the expansionmember. The same advantageous effects can be obtained in the presentembodiment as in the first embodiment.

FIG. 5 shows a Mollier diagram of a heat pump 20B used in the presentembodiment, under the medium temperature condition. In this diagram, abroken line shows a Mollier diagram of a heat pump without a liquidcooling heat exchanger.

In the heat pump without the liquid cooling heat exchanger, the enthalpyof the refrigerant at the inlet of the expander is H3′, and the enthalpyof the refrigerant at the outlet of the expander, where the refrigeranthas undergone adiabatic expansion changes (isentropic changes) from D′to F′, is H2′. On the other hand, in the heat pump 20B used in thepresent embodiment, after passing through the radiator 22, therefrigerant lowers its temperature in the internal heat exchanger 23A,then is warmed to Point E in the liquid cooling heat exchanger 24, anddrawn into the expander 25B. At this time, the enthalpy of therefrigerant at the inlet of the expander 25B is H3, and the enthalpy ofthe refrigerant at the outlet of the expander 25B, where the refrigeranthas undergone adiabatic expansion changes from D to F, is H2.

Generally, the enthalpy change (ΔH) during the adiabatic expansionchanges increases as the enthalpy of a refrigerant drawn into anexpander increases. The energy of power that can be recovered by theexpander is proportional to this enthalpy change. Therefore, the energyof power that can be recovered by the expander increases as the enthalpyof the refrigerant drawn into the expander increases. Therefore, theexpansion energy that can be recovered by the expander 25A used in thepresent embodiment is much greater than the expansion energy that can berecovered by the expander in the heat pump without the liquid coolingheat exchanger. As a result, by using the recovered expansion energy as,for example, a part of the power input to the compressor 21, the COP ofthe heat pump 20B can be improved dramatically.

Furthermore, since the optimum high pressure can be lowered in therefrigerant circuit 3 of the present embodiment, the difference betweenthe high pressure and the low pressure that acts on the expander 25B canbe reduced. Therefore, the leakage loss of the refrigerant and thefriction loss are reduced, and thus the efficiency of the expander 25Bcan be improved. As a result, more expansion energy can be obtained.

Third Embodiment

FIG. 6 shows a heat pump heating system 1C according to the thirdembodiment of the present invention. The heat pump heating system 1C ofthe present embodiment is different from the heat pump heating system 1Aof the first embodiment in that an ejector 25C is used as the expansionmember.

Specifically, the ejector 25C is connected to the radiator 22 by thesecond pipe 32 and to the evaporator 26 by the third pipe 33. Agas-liquid separator 27 is provided in the middle of the third pipe 33.Furthermore, the evaporator 26 is connected to the ejector 25C by adivided fourth pipe 34A, and the gas phase portion of the gas-liquidseparator 27 is connected to the compressor 21 by a divided fourth pipe34B. In the present embodiment, the internal heat exchanger 23A isprovided so as to bundle the second pipe 32 and the divided fourth pipe34B.

In the present embodiment, the refrigerant that has passed through theinternal heat exchanger 23A and the liquid cooling heat exchanger 24flows into the ejector 25C and expands there. The refrigerant flowingout of the ejector 25C is separated into a gas refrigerant and a liquidrefrigerant. The liquid refrigerant is fed to the evaporator 26 andevaporated there, and then flows into the ejector 25C again. On theother hand, the gas refrigerant separated by the gas-liquid separator 27flows into the internal heat exchanger 23A and is heated there by therefrigerant that has released heat in the radiator 22. The otheroperations and actions of the refrigerant and water are the same asthose in the first embodiment.

The same advantageous effects can be obtained in the present embodimentas in the first embodiment. Furthermore, according to the presentembodiment, the expansion energy can be increased, as in the secondembodiment. Therefore, the flow velocity of the refrigerant in theejector 25C can be increased, and thus the pressure of the refrigerantdrawn into the compressor 21 can further be increased. Accordingly, thecompression power required for the compressor 21 can be reduced, andthus the COP of the heat pump 20C can be improved.

Fourth Embodiment

FIG. 7 shows a heat pump heating system 1D according to the fourthembodiment of the present invention. The heat pump heating system 1D ofthe present embodiment is different from the heat pump heating system 1Aof the first embodiment in that the circulation path 5 is provided witha hot water storage tank 50 instead of the heater 4.

The hot water storage tank 50 is a vertically extending cylindricalclosed casing and is filled with water. The lower portion of the hotwater storage tank 50 is connected to the liquid cooling heat exchanger24 by the supply pipe 51, and the upper portion thereof is connected tothe radiator 22 by the recovery pipe 53. When the pump 62 is rotated,the water is introduced from the lower portion of the hot water storagetank 50 to the liquid cooling heat exchanger 24 through the supply pipe31, and the water in the form of hot water is introduced from theradiator 22 to the upper portion of the hot water storage tank 50through the recovery pipe 53. Thereby, the hot water is stored in thehot water storage tank 50 from the top. Furthermore, in the presentembodiment, the temperature of the water flowing into the supply pipe 51from the hot water storage tank 51 is detected by the temperature sensor61 provided in the supply pipe 51.

On the other hand, the heater 4 is connected to the upper portion of thehot water storage tank 50 by a feed pipe 81, and to the lower portion ofthe hot water storage tank 50 by a return pipe 82. In the presentembodiment, a heating pump 65 is provided in the return pipe 82, but theheating pump 65 may be provided in the feed pipe 81. The heating pump 65is connected to the controller 6. When the heating pump 65 is rotated,the hot water stored in the hot water storage tank 50 is fed to theheater 4 through the feed pipe 81, and the hot water that has releasedheat in the heater 4 is returned to the hot water storage tank 50. Thatis, the hot water storage tank 50, the feed pipe 81, the heater 4, andthe return pipe 82 constitute a heating circuit 8.

Next, the control performed by the controller 6 is describedspecifically.

<Hot Water Storage Operation>

When the controller 6 determines, with a sensor (not shown) provided inthe hot water storage tank 50, that the amount of hot water left in thehot water storage tank 50 is insufficient, it operates the heat pump 20Aand rotates the pump 62. Thereby, the water is heated in the radiator 22to produce hot water, and this hot water is fed to the hot water storagetank 50 for the storage of hot water.

During this hot water storage operation, the controller 6 uses thetemperature sensor 61 to monitor the temperature of the water flowinginto the supply pipe 51. When the water temperature detected by thetemperature sensor 61 is lower than a predetermined temperature (lowtemperature condition), the controller 6 controls the three-way valve 63so that the water is circulated through the bypass pipe 54.Specifically, the controller 6 sets the three-way valve 63 so that thebypass pipe 54 is communicated with the upstream part 51 a of thethree-way valve 63 in the supply pipe 51. As a result, the first routepassing only through the radiator 22 is selected.

In the low temperature condition, the refrigerant circulating throughthe refrigerant circuit 3 operates in the same manner as in the firstembodiment. On the other hand, the water circulating through thecirculation path 5 (first route) is heated in the radiator 22, and theresulting hot water is stored in the hot water storage tank 50. Thewater is taken from the lower portion of the hot water storage tank 50,and then flows into the radiator 22 again, where it is heated to hotwater.

Conversely, when the water temperature detected by the temperaturesensor 61 is equal to or higher than the above predetermined temperature(medium temperature condition), the controller 6 controls the three-wayvalve 63 so that the water is circulated not through the bypass pipe 54.Specifically, the controller 6 sets the three-way valve 63 so that theupstream part 51 a and the downstream part 51 b of the three-way valve63 in the supply pipe 51 are communicated with each other. As a result,the second route passing through both of the liquid cooling heatexchanger 24 and the radiator 22 is selected.

In the medium temperature condition, the water flowing into the liquidcooling heat exchanger 24 has a higher temperature than the refrigerantflowing into the liquid cooling heat exchanger 24. The refrigerantcirculating through the refrigerant circuit 3 operates in the samemanner as in the first embodiment. On the other hand, the watercirculating through the circulation path 5 (second route) is heated inthe radiator 22, and the resulting hot water is stored in the hot waterstorage tank 50. Medium temperature water that has not releasedsufficient heat in the heater 4 is stored in the lower portion of thehot water storage tank 50. The medium temperature water is taken fromthe lower portion of the hot water storage tank 50, and flows into theliquid cooling heat exchanger 24, where it exchanges heat with therefrigerant flowing out of the internal heat exchanger 23A. As a result,the water is cooled to a low temperature state. The low temperaturewater flows into the radiator 22 again and is heated to hot water.

<Heating Operation>

When a user turns on a heating switch (not shown), for example, thecontroller 6 rotates the heating pump 65. Thereby, the hot water storedin the hot water storage tank 50 is fed to the heater 4 for performingheating.

The same advantageous effects can be obtained in the present embodimentas in the first embodiment. In the present embodiment, the heated hotwater can be stored once in the hot water storage tank 50. Therefore,for example, in the case where heating is interrupted and then resumed,the hot water stored in the hot water storage tank 50 can be fed to theheater 4 before the water that has cooled down during the interruptionof the heating operation is reheated in the heat pump 20A, and therebythe heating operation can be resumed quickly.

Furthermore, according to the present embodiment, high temperature hotwater can be produced at low electricity prices during night hours andthis hot water can be stored in the hot water storage tank 50.Therefore, the running cost of the heating operation can be reduced.

<Modification>

A water inlet pipe 91 (see FIG. 8) for supplying tap water to the hotwater storage tank 50 may be provided in the hot water storage tank 50.With this structure, the temperature of hot water flowing into theheater 4 can be controlled freely by mixing tap water and hot waterflowing into the heater 4 or exchanging heat between them. Furthermore,since tap water can be used to control the temperature of water flowinginto the heater 4, the optimum temperature water is allowed to flow intothe heater 4 even if the temperature of hot water stored in the hotwater storage tank 50 is higher than that of hot water to be used in theheater 4. As a result, the amount of heat stored in the hot waterstorage tank 50 can be increased. Therefore, even if the operation ofthe heat pump 20A is stopped for a long time, heating operation can becontinued in the heating circuit 8. Alternatively, a mixing valve 91 maybe provided in the feed pipe 81 to connect the water inlet pipe 91 tothis mixing valve.

A hot water outlet pipe 92 (see FIG. 8) for withdrawing hot water fromthe hot water storage tank 50 also may be provided in the hot waterstorage tank 50.

With this structure, hot water also can be supplied during heatingoperation.

Needless to say, the heat pump 20B shown in FIG. 4 using the expander25B as the expansion member or the heat pump 20C shown in FIG. 6 usingthe ejector 25C as the expansion member can be used in the embodimentdescribed above.

Fifth Embodiment

FIG. 8 shows a heat pump heating system 1E according to the fifthembodiment of the present invention. The heat pump heating system 1E ofthe present embodiment is different from the heat pump heating system 1Dof the fourth embodiment in that an in-tank heat exchanger 83 isdisposed in the hot water storage tank 50. Furthermore, the water inletpipe 91 is connected to the lower portion of the hot water storage tank50, and the hot water outlet pipe 92 is connected to the upper portionof the hot water storage tank 50.

The in-tank heat exchanger 83 is designed to heat a heat carrier that isa second liquid by means of the hot water stored in the hot waterstorage tank 50. The in-tank heat exchanger 83 is connected to theheater 4 by the feed pipe 81 and the return pipe 82. When the heatingpump 65 is rotated, the heat carrier that has been heated in the in-tankheat exchanger 83 is fed to the heater 4 through the feed pipe 81, andthe heat carrier that has released heat in the heater 4 is returned tothe in-tank heat exchanger 83 through the return pipe 82. As the heatcarrier, for example, an antifreeze liquid can be used, but waterpreferably is used because it is available at low cost and in largequantities.

Since the controller 6 performs control in the same manner as in thefourth embodiment, the description thereof is not repeated here. Itshould be noted, however, that during the heating operation, the heatcarrier that has exchanged heat with the hot water stored in the hotwater storage tank 50 releases heat in the heater 4, that is, the heatof the hot water is dissipated through the heat carrier in the heater 4,and thereby heating is performed.

The same advantageous effects can be obtained in the present embodimentas in the fourth embodiment.

Sixth Embodiment

FIG. 9 shows a heat pump heating system 1F according to the sixthembodiment of the present invention. The heat pump heating system 1F ofthe present embodiment includes a structure for hot water supply inaddition to the heat pump heating system 1D of the fourth embodiment.Specifically, a hot water supply heat exchanger 93 is disposed in thehot water storage tank 50, and the water inlet pipe 91 and the hot wateroutlet pipe 92 are connected to this hot water supply heat exchanger 93.That is, in the present embodiment, tap water flowing from the waterinlet pipe 91 to the hot water outlet pipe 92 is heated by means of hotwater in the hot water storage tank 50 so as to produce hot water.

INDUSTRIAL APPLICABILITY

The heat pump heating system of the present invention is useful as ameans for improving the COP of a heat pump through the use of mediumtemperature water produced in a heater.

1-12. (canceled)
 13. A method of controlling a heat pump heating system,comprising: circulating a refrigerant in a refrigerant circuit, therefrigerant circuit including a compressor, a radiator, a liquid coolingheat exchanger, an expansion member, an evaporator and an internal heatexchanger; circulating a liquid in a circulation path, the circulationpath including a heater, a supply pipe that introduces a liquid from theheater to the liquid cooling heat exchanger, an intermediate pipe thatintroduces the liquid from the liquid cooling heat exchanger to theradiator, and a recovery pipe that introduces the liquid heated by theradiator to the heater; expanding a high pressure refrigerant to a lowpressure refrigerant at the expansion member; causing the low pressurerefrigerant to absorb heat at the evaporator; transferring heat from ahigh pressure refrigerant that has released heat at the radiator to thelower pressure refrigerant at the internal heat exchanger of therefrigerant circuit; compressing the low pressure refrigerant into thehigh pressure refrigerant with the compressor; transferring heat fromthe liquid in the circulation path to the high pressure refrigerant inthe refrigerant circuit at the liquid cooling heat exchanger;transferring heat from the high pressure refrigerant in the refrigerantcircuit to the liquid in the circulation path at the radiator, andproducing a heated liquid in the circulation path; and dissipating heatfrom the heated liquid in the circulation path at the heater downstreamof the radiator.
 14. The method according to claim 13, furthercomprising: inhibiting heat exchange between the heated liquid and thehigh pressure refrigerant at the liquid cooling heat exchanger when theheated liquid flowing in the supply pipe has a temperature equal to orlower than the temperature of the high pressure refrigerant flowing intothe liquid cooling heat exchanger.
 15. The method according to claim 13,wherein the internal heat exchanger is configured to exchange heatbetween the high pressure refrigerant flowing out of the radiator andthe low pressure refrigerant flowing out of the evaporator.
 16. Themethod according to claim 13, wherein the internal heat exchanger isconfigured to exchange heat between the high pressure refrigerantflowing out of the radiator and the low pressure refrigerant beforeflowing into the evaporator.
 17. The method according to claim 13,wherein the circulation path further includes a bypass pipe connectingthe supply pipe and the intermediate pipe, and a switching member forswitching between a circulation of the liquid not through the bypasspipe and a circulation of the liquid through the bypass pipe; the methodfurther comprising: preventing the heated liquid from circulatingthrough the bypass pipe by the switching member, and thereby performingheat exchange between the heated liquid and the high pressurerefrigerant at the liquid cooling heat exchanger, when the heated liquidflowing in the supply pipe has a temperature higher than the temperatureof the high pressure refrigerant flowing into the liquid cooling heatexchanger, or directing the heated liquid through the bypass pipe by theswitching member, and thereby inhibiting heat exchange between theheated liquid and the high pressure refrigerant at the liquid coolingheat exchanger, when the heated liquid flowing in the supply pipe has atemperature equal to or lower than the temperature of the high pressurerefrigerant flowing into the liquid cooling heat exchanger.
 18. Themethod according to claim 13, wherein the supply pipe includes atemperature sensor that detects the temperature of the liquid flowinginto the supply pipe.
 19. The method according to claim 13, wherein therefrigerant is carbon dioxide.